LIQUID -SOLID MASS TRANSFER UNDER FORCED CONVECTION

Abstract

The present work deals with the study of the rate of mass transfer at the inner surface of an annuli under developing flow conditions. The study was carried out using an electrochemical technique which involves measuring limiting current of the cathodic reduction of K3Fe(CN)6 at a Nickel plated cylinder.

Variables studied were physical properties of the solution (p, µ and D), ' liquid velocity, surface roughness, inlet port diameter, and the length of the working section from the inlet port. The study rev�aled the following results: 1. The mass transfer coefficient increases with liquid flow rate

according to the equations:

K= a1 y0.55 K = a2 y0.�5

K=a3 V

for smooth surface and V < 10 cm/s ' for smooth surface and V > 14 cm/s ! for rough surface and V > 1 fl- cm/s

2. Surface roughness was found to increase the: rate of mass transfer by an amount ranging from 10 % to 211 % depending on Re and roughness height (e). Only rough surfaces with roughness height larger than the laminar sublayer can enhance the rate of mass transfer. 3. Mathematical treatment of the mass transfer data using the ' method of dimensional analysis resulted in the following correlations: